Method of dissolving binary alloys



United States Patent li IETHOD OF DISSOLVING BINARY ALLOYS No Drawing. Application December 22, 1954, Serial No. 477,145

5 Claims. (Cl. 75-121) This application deals with a process of dissolving binary uranium alloys, and in particular binary uranium alloys which contain comparatively small quantities of zirconium.

Zirconium-uranium alloys are being used as fuel material in some types of neutronic reactors. The fuel elements have to be dissolved either after irradiation for recovery of the various ingredients and for analytical purposes, or sometimes after inspection when the fuel elements have been found flawy and the metals are to be recovered.

Zirconium-containing binary uranium alloys have been dissolved heretofore in nitric acid. However, the nitric acid, for instance, of a concentration between 7 and 15 M, was found to dissolve the uranium faster than the zirconium whereby a highly reactive zirconium surface was obtained on the alloy bodies. This reactive surface proved to be pyrophoric. If the surface, for instance, was struck with a pointed rod a vigorous reaction took place with evolution of heat and light and forceful ejection of the container contents. Violent shaking produced similar results. Sometimes serious explosions were caused by this phenomenon.

It is an object of this invention to provide a process for dissolving binary zirconium-uranium alloys by which the two components are dissolved at the same rate.

It is another object of this invention to provide a process for dissolving binary zirconium-uranium alloys which is not hazardous.

It is still another object of this invention to provide a process for dissolving binary zirconium-uranium alloys with a solvent that does not corrode stainless steel equipment. I

These objects are accomplished by immersing the zirconium-uranium alloy in an aqueous solution of a mixture consisting of nitric acid, hydrofluoric acid and aluminum nitrate.

The concentrations of the ingredients may vary widely. For instance, the nitric acid concentration may range between 7 and 15 M, the hydrofluoric acid may be present in a concentration between 0.02 and 0.5 M and the Patented Aug. 7, 1956 aluminum nitrate in a concentration between 0.5 and 1.5 M. The quantity of the solvent is, of course, dependent upon these concentrations. A ratio of 4 moles hydrofluoric acid per mole of zirconium has given satisfactory results, and within the concentration ranges given above the use of 4 liters of solution per kilogram of alloy was found adequate. While the dissolution may be carried out at room temperature, heating of the solution, preferably to between and 0, proved advantageous.

Substitution of ammonium silicofiuoride for the hydrofluoric acid gave also satisfactory results; the preferred concentration of the ammonium silicofiuoride was about 0.1 M.

Example A (SO-gram piece of a uranium alloy containing 2% by weight of zirconium and 98% by weight of uranium was immersed in an aqueous nitric acid-hydrofluoric acidaluminum nitrate solution; the concentrations were 11 M for the nitric acid, 0.3 M for the hydrofluoric acid and 0.75 M for the aluminum nitrate. The process was carried out in a stainless steel container. After about 10 hours practically all of the alloy had dissolved, with the exception of a small residue which weighed less than 6 mg. There was no explosion-like phenomenon and no corrosion of the stainless steel took place.

The process of this invention was found to be applicable to binary uranium alloys which contain up to 20% by weight of zirconium.

It will be understood that this invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

l. A process of dissolving binary zirconium-uranium alloys containing up to 20% by weight of zirconium consisting of immersing the alloy in an aqueous solution of nitric acid, hydrofluoric acid and aluminum nitrate.

2. The process of claim 1 in which immersion is carried out at elevated temperature.

3. The process of claim 2 in which the temperature ranges between 90 and 100 C.

4. The process of claim 1 in which the nitric acid is present in the aqueous solution in a concentration of from 7 to 15 M, the hydrofluoric acid in a concentration between 0.02 and 0.5 M and the aluminum nitrate in a concentration of between 0.5 and 1.5 M.

5. The process of claim 4 in which the aqueous solution contains nitric acid in a concentration of 11M, hydrofluoric acid in a concentration of 0.3 M and aluminum nitrate in a concentration of 0.75 M.

References Cited in the file of this patent Milner et al.: Analyst, vol. 79, pp. 475-482 (1954). (Copy in Scientific Library.) 

1. A PROCESS OF DISSOLVING BINARY ZIRCONIUM-URANIUM ALLOYS CONTAINING UP TO 20% BY WEIGHT OF ZIRCONIUM CONSISTING OF IMMERSING THE ALLOY IN AN AQUEOUS SOLUTION OF NITRIC ACID, HYDROFLUORIC ACID AND ALUMINUM NITRATE. 